1. Field of the Invention
The present invention relates to a moisture sensor, a moisture detector, and an image forming apparatus.
2. Description of the Related Art
In factories manufacturing foods or clothing, moisture sensors for detecting a moisture content of a product are used.
For example, Japanese Patent No. 3529516 discloses an optical measuring apparatus including a rotating plate that is installed obliquely to a light-projecting axis of a light source, has a filter and a reflector, and projects light onto a target of measurement through the filter when a measurement is to be conducted, a reflecting unit that folds and reflects the light reflected on the reflector included in the rotating plate so that the light passes through the filter on the rotating plate when no measurement is conducted, a collecting unit that collects the light from the target of measurement or the light from the reflecting unit and guides the light to a detecting element, and an operating unit that applies a correcting operation to an output of the detecting element.
Japanese Translation of PCT International Application Publication No. 2010-536050 discloses a method and an apparatus for electromagnetic detection for measuring parameters such as the moisture content or the basis weight of a fibrous web, e.g., paper or a non-woven.
Japanese Translation of PCT International Application Publication No. 2008-539422 discloses a sensor for measuring at least one component in a composition.
Japanese Patent No. 4499341 discloses a biometric authentication apparatus including an illuminating unit that outputs light having oscillation direction limited to one direction, and a blocking unit that blocks reflected light in a direction perpendicular to the oscillating direction of the light output from the illuminating unit.
Japanese Laid-open Patent Publication No. 10-260142 discloses an image evaluation apparatus including an illuminating unit that illuminates an image to be evaluated with parallel light rays having a linear polarization characteristic of either p-polarization or s-polarization, and a polarizing element that separates reflected light from the image to be evaluated into reflected light having a polarization plane that is on the same plane as the polarization plane of the illumination and reflected light having a polarization plane perpendicular to the polarization plane of the illumination.
Therefore, there is a need for a moisture sensor having a small size and providing high-precision measurement.